On Mon, 02 Aug 2010 23:33:23 +0100, John Rumm
wrote:

I doubt a bit of crushing makes that much difference...

It must eventually make a difference because if crushed enough. This
really was a bent and squashed all over the place. Even if the damage
had not affected its u-value, it certainly was not "first" grade.
Since I was paying for "firsts", I didn't want to be sent a second!

I was gluing it into the window reveal so I wanted it to be as
straight as possible.

Never seen an official one. A standard hardpoint jacksaw seems to work
fast enough.

There is one but I have been too lazy to register on the celotex site
to read the spec. It's also listed on the toolstation web site but
they don't go into details. I wasn't going to buy one especially but I
thought if I knew the tpi, I could match it to the nearest saw I had
next time.